1. Field of the Invention
This invention relates to an electric power supply for a heater, in particular relates to an electric power supply for a heater heating a catalyst for the use of purifying exhaust gas from an internal combustion engine of the vehicle.
2. Description of the Related Art
Catalyst for the use of purifying exhaust gas from an internal combustion engine is not usually activated under a predetermined value of temperature so as not to be able to purify the exhaust gas. In particular, the catalyst without the heater is heated by heat of the exhaust gas. Therefore, since the exhaust gas is low temperature and the inner portion of the internal combustion engine is not heated when the internal combustion engine is started, the catalyst can not sufficiently purify the exhaust gas.
A conventional catalytic device which comprises a heater coated with the catalyst is disclosed in the Japanese Patent Laid Open No. 48 (1973)-54312. In accordance with the catalytic device disclosed in the prior art ingredients not burned in the exhaust gas are evaporated by the heater when-the engine is started.
However, according to the catalytic device because a large amount of the rush current (which will be described "electric current" hereinafter) is flowed from a battery activating the heater when the heater is heated, the battery has a short life. Further, the battery has to include a large capacity.
A conventional electric power supply for a heater heating a catalyst is disclosed in the Japanese Patent Laid Open No. 4 (1992)-276111. The electric power supply in the prior art comprises a charged condenser used for the power supply to the heater. The charged condenser is charged up to the same voltage of the battery by the battery directly. Therefore, the electric current is not flowed from the battery activating the heater when the heater is heated. Further, early in the activation of the heater the condenser can flow a large electric current into the heater relative to the battery. Consequently, the electric power supply can rapidly heat the catalyst.
However in accordance with the prior art, since the heater is heated by the voltage of the battery, a large amount of the electric current has to be flowed into the heater so as to heat the catalyst when the condenser is charged by the battery. Therefore, the voltage applied to the heater is decreased through a cable and switches and so on. Furthermore, the electric power supply has to be large in size, heavy in weight and high in cost.
In case of the electric power supply including two heaters each of heating two catalysts provided to be in parallel each other so as to be arranged with the exhaust passage, a large amount of electric current is flowed into the heaters from the battery because of the low resistance of the heaters. Therefore, the cable and the switches are required to be used for a large electric current exclusively.